Novel polyurethane elastic filaments and yarns and process for producing the same



United States Patent Ofiice 3,331,887 Patented July 1%, 1967 This invention relates to novel polyurethane elastic filaments and yarns and a process for producing same.

(3) A polymer having 2 urethane linkages produced by employing glycols as a chain-extender, in the crystalline part;

However, polymers (1) and (2) are disadvantageous in that they exhibit low resistance to bleaching and low light fastness and the polymer (3) is disadvantageous in its low resistance to heat and mechanical properties.

By contrast, the present polymers have repeating structural units represented by the formula:

o o 0 o 0 II II II II II More particularly, this invention relates to novel polyurethane elastic filaments and yarns consisting of repeating structural units represented by the formula 0 o o o 0 ll 1! II H H wherein R is a bivalent organic radical such as 1,3-phenylene, 1,4-phenylene, 2,4-tolylene, 2,6-tolylene, 4,4-biphenylene, 2,2-dimethyl-4,4-biphenylene, 3,3'-dimethyl-4,4-

wherein R and R represent respectively a bivalent organic residue and A represents a bivalent polymer residue, said filaments and yarns having improved characteristics in mechanical properties such as elastic recovery, light fastness and chemical properties.

Polyurethanes have been produced in steadily increasing quantities and grades in recent years and because of their unique properties in elasticity, polyurethanes are useful in wide variety of applications in the form of yarns. However, it is generally considered that polyurethane filaments and yarns made by combining the conventionally known prepolymers with the compounds having bifunctional active hydrogen atoms have not been satisfactory in elastic recovery, strength, resistance to solvents.

An object of this invention is to provide elastic polyurethane filaments and yarns having an improved elastic recovery, strength and resistance to solvents, in comparison with conventional yarns made by combining conventional prepolymers with compounds having bifunctional active hydrogen atoms even without further subjecting the resultant yarn to a cross linking treatment.

Another object of this invention is to provide other polyurethane elastic filament yarns which can be obtained by subjecting the foregoing filaments and yarns to a cross-linking step, having additional advantageous properties such as insolubility in hot dirnethyl formamide and hot dimethyl sulfoxide, higher light fastness, increase in elastic recovery, tensile strength and tensile elongation.

As the conventional polyurethane useful for filaments and yarns there have been the following types:

(1) A polymer having a bisureine linkage produced by employing hydrazine as a chain-extender, in the crystalline part;

(2) A polymer having 2 urea linkages produced by employing diamines as a chain-extender, in the crystalline part;

biphenylene, 4,4'-diphenylmethane, 3,3-dimethyl-4,4-diphenylrnethane, 1,5-naphthylene, 1,8-naphthylene, trimethylene, tetramethylene, pentarnethylene and hexamethylene radicals; R is a bivalent organic radical such as ethylene, propylene, iso-propylene and n-butylene radicals; A is a bivalent polymer residue such as polyester residue, polyether residue and poly(oxyalkylene-carboxyalkylene) residue. These filaments and yarns have the following properties:

Tensile strength g./d 0.50-0.95 Tensile elongation "percent..- 600-1100 40 Creep recovery do 90-99.5 Denier Variable Light-fastness Good Chemical properties Good Melting point C. 180-210 Intrinsic viscosity (in dimethylformamide) 0.8-1.2 Specific gravity 1.0-1.2

The raw materials employed in the present invention have respective features toward the properties of the elastic fibers produced from the raw materials. Typical examples therewith will be described as follows.

Efiect of kind of diisocyanatets' Effect of aminloalcohols Aminoalcohols having an amino group and a hydroxyl group at the w, w positions of a linear aliphatic hydrocarbon having 2-6 carbon atoms, especially 2-3 carbon atoms is properly employed.

7 Aromatic aminoalcohol is insufficient in its reactivity and besides the elastic fiber resulting from the use thereof is defective in that the fiber is stained by sunlight.

Aminoalcohols containing a substituent group, even in an aliphatic aminoalcohol is liable to make the intermolecular force of the elastic fiber therefrom lower; thereby causing deformation by an external force.

Efiect of kind of cross-linking agents Dimethylol urea-Formalin: improves resistance to solvents and chemicals, tensile strength and modulus, but since the cross-linking condition is considerably drastic, the fiber surface becomes hard and the fiber becomes brittle.

Paraformaldehyde-Formalin: cross-linking is effected in mild condition; accordingly various mechanical and.

chemical properties are extremely improved.

Efiect of kind of diol polymers Representative examples of the diol polymers are polyester glycol, polyether glycol and poly(oxyalkylene-carboxyalkylene) glycol.

Diol polymers having side chains such as polypropylene glycol decrease tensile strength and increase stress relaxa tion in stretching of the elastic fiber therefrom. Diol polymers not having side chains improve mechanical properties such as tensile strength and stress relaxation of the fiber. However, when such diol polymers come to have a molecular weight above about 1500, permanent set at low temperature becomes greater. Diols of the polyester type have a weakness in chemical properties, especially in resistance to acid and base, but dialsof the polyether type and lactone polyester type improve these properties. Diols having ether linkages and ester linkages in the main chain such as poly-oxyalkylene-carboxyalkylene) glycol are liable to improve the permanent set at low temperature when compared with those having either ether linkages or ester linkages in the main chain. 7

The present polyurethane filaments and yarns are produced in accordance with the following procedures:

A prepolymer obtained by adding a linear hydroxylterminated polymer to more than anequivalent amount of an organic diisocyanate,-is dissolved in an organic.

solvent. An aminoalcohol is added to this solution in an amount equivalent to the isocyanate radicals remaining in the above prepolymer and reacting only the amino radicals of the aminoalcohol with the isocyanate radical to yield a low'molecular polymer having terminal hydroxy radical..(Hereinafter referred to as macrodiol.) To this macrodiol an almost equivalent amount of an organic diisocyanate .is added and subjected to polymerization. Polyurethane elastic filaments and yarns are obtained by spinning the resulting polymer. Another type of polyurethane elastic filaments and yarns having an appropriate degree of three dimensional, network structure is obtained by treating theabove-mentioned elastic filaments and yarns witha cross linking agent. The process of this invention is described in greater detail below.

The process of this invention consists of four steps. The first step is the preparation of a prepolymer. The prepolymer is prepared by reacting a linear bifunctional hydroxyl-terminated polymer having a melting point below about 50 C. and a molecular weight between 800 and 2500 with an organic diisocyanate in a ratio of isocyanate radical to hydroxyl. radical of 1.0 -2.0:1.0, preferably 1.3-2.0:1.0.

As an example, one mole of a linear hydroxy-terminated polymer (hereinafter referred to as a diol polymer) is reacted with two moles of 4,4'-diphenylrnethane diisocyaare regularly arranged. The crystalline part has 4 urethane linkages and 2 urea linkages .and the urethane linkage is separated from a urea linkage-by ethylene radical.

When the molar ratio of organic diisocyanate to diol polymer varies within the range from 2.0 to 1.0, a radical having 2 urethane linkages, represented by the formula;

is introduced into the non-crystalline part by connecting diol polymer parts. But when the ratio of isocyanate radical to hydroxy radical becomes 1, the creep recovery ofyarn becomes almost unnoticeable. We have found that r a molar ratio of isocyanate radical to hydroxy radical is most preferable in the range from 1.3 to 2.0.

In the preparation of a prepolymer, it is found necessary to be=particularly attentive to the following points. In order to avoid gelatination strictly in the step of preparing a spinning solution, it is necessary to choose. such conditions that only induce the reaction of the isocyanate radicals with the hydroxy radicals and that do not produce allophanate linkages, biuret linkages and the like. Namely when a linear hydroxyl-terminated polymer such as a diol polymer is mixed with an organic diisocyanate, it is necessary to avoid such a condition as to, react an organic diisocyanate locally with an excess of a diol polymer, e.g. to add an organic diisocyanate into a fused diol polymer or "a condition which induces biuret linkages due to'the presence of a large amount of water in the diol polymer. Accordingly it is generally preferable to maintain the acid number of the diol polymer as Well as the water, content ata low value in the present process. As a reaction condition, the usual condition i.e. a temperature of 60150 C. for 1 to 2 hours, preferably C;

for 1 to 2 hours without a catalyst, is used. This reaction a glycol, polyether glycol, and poly(oxyalkylene-carboxyalkylene) glycol are effectively used. In carrying out the above-mentioned reaction, known catalysts e.g. tertiary amines, such as triethylene amine; or organo-metallic compounds such as dibutyl tin-dilaurate may be used.

The second step consists of dissolving the prepolymer obtained in the first step in an organic solvent to produce a homogeneous solution and reacting the resulting prepolymer solution with an aminoalcohol in amounts equivalent to the isocyanate in the prepolymer to produce a macrodiol of a low molecular hydroxyl-termin'ated polymer. This step is the essential part of the present invention which is considered to be a necessary condition for constituting an invention. As an organic solvent for the prepolymer in the second step, dioxane, acetone, methyl ethylketone, benzene, toluene, dimethyl formamide, dimethyl acetamide, and dimethyl sulfoxide areused singly or as a mixture. As an aminoalcohol, ethanolamine, propanolamine, isopropanolamine and n-butanol'amine, are effectively used.

The amount of the arninoalcohol is preferably equal to the isocyanate radicals in the above mentioned prepolymer. When the amount is excessive, unreacted aminoalcohol remains. And when it is insuflicient, the free isocyanate radicals still remaining after the reaction with amino radicals is completed is allowed to react gradually with hydroxy radicals. In either case, the following step of chain extending which uses a diisocyanate as connecting agent does not proceed smoothly and the quality of the resulting polymer shows deterioration.

In order to make the length of the crystalline part longer, an aminoalcohol is used in this invention. When a diamine is used instead of this, both terminals are occupied by amino radicals, the crystalline part of polymers connected by the diisocyanate contains 4 urea linkages and the quality of polymers generally shows deterioration when the cross-linking reaction is applied to it, probably due to an increase of cross linking points. In most of these cases a decrease of elongation is inevitable and it is difiicult to obtain reproducible elastic filaments and yarns. However, according to the present process which is characterized by using an aminoalcohol, none of such defects are recognized and it is easy to obtain high quality filaments and yarns with reproducibility. The description on the second step continues as follows. The prepolymer obtained in the first step is cooled to about room temperature, and brought to a homogeneous solution by the addition of dehydrated, purified dirnethylformamide. Dropping this solution into a dimethyl formamide solution of aminoalcohol, the amount of which is equivalent to the isocyanate radicals, a macrodiol solution can be obtained. If the above solution is introduced into a large amount of ethanol, stirred with cooling at a very low temperature, a white solid substance begins to be separated gradually. After filtration, washing with a small amount of ethanol and drying at a reduced pressure, a macrodiol is separated. This substance is a stable compound whose terminal hydroxy radicals can be determined quantitatively by the acetylation method and which shows a definite melting point. For example, 300 g. of dimethyl formaldehyde solution of a macrodiol obtained in Example 1 (which will be later given) is dropped into 2.5 l. of 95 percent ethanol at room temperature with stirring. Further vigorous stirring is continued for 30 minutes. Subsequently this solution is cooled to C. by use of ice water-salt mixture. The separated white substance is filtered, washed with a small amount of cold ethanol several times and dried at a reduced pressure until it does not show any further decrease of weight. The resulting macrodiol has a melting point between 38 C. and 39 C. The average molecular weight determined by the acetylation method is 2,450 (the theoretical molecular weight is 2,320). The OH number is 45.85 and the acid number is 0.

The macrodiol obtained in the second step is transferred to the third step.

The third step consists of reacting the macrodiol with an organic diisocyanate. In this step the macrodiol can be used either by taking out and dissolving in a suitable solvent such as dimethyl formamide or the like or as it is Without taking out. In either case, an organic diisocyanate is added in an amount equivalent to the macrodiol in the solution or in a slight excess, and after suificient stirring in the absence of a catalyst or in the presence of a known catalyst which accelerates the reaction between the NCO radical and the 0H radical, e.g. such as trimethylene diamine, dibutyl tin dilaurate, polymerization is carried out at a suitable temperature with or without stirring. It does not matter whether the organic diisocyanate added at this time is the same as the one used in the preparation of the prepolymer in the first step or not. Generally speaking, the diisocyanate used in preparing the prepolymer can be aromatic or aliphatic, but it is preferable that the organic diisocyanate used in the third step be aromatic. As an aromatic diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6- tolylene diisocyanate, 4,4'-biphenylene diisocyanate, 2,2- dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethyl- 4,4'-diphenylmethane diisocy-anate, 1,5-naphthylene diisocyanate and 1,8-naphthylene diisocyanate are effectively used. As an aliphatic diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate and hexamethylene diisocyanate can be effectively used.

It is most preferable that the amount of organic diisocyanate to be added is cont-rolled so as to be in a ratio of hydroxy radical of macrodiol to isocyanate radical of the organic diisocyanate ranging of from 1.00 to 1.04. When this ratio is smaller than 1, a high molecular weight polymer cannot be obtained. As this ratio becomes larger than 1, gelatination occurs and deteriorates the quality of the resulting elastic yarns.

The fourth step consists of spinning the polymer solution obtained in the third step to yield polyurethane yarns, and if required, the resulting yarns are subjected to a cross linking step. Yarns and filaments of this invention are prepared by either wet or dry spinning. In the spinning the following conditions are employed.

Wet spinning process:

Orifice of spinneret: its dimension is freely variable,

but preferable in the range of 0.04 mm.0.l5

Spinning velocity: 5-60 m./min., especially 20-30 rn./min.

Polymer concentration of spinning solution: 15-

30%, especially 20-25%.

Coagulation bath: DMF aq. solution, water, methanol, aq. Na CO solution, etc., bath temperature 40-60 C., spinning depth 3-5 m.

Draft ratio: 0.5-2.0

Bath temperature: 50-70 C., especially 4060 C.

Dry spinning process:

Orifice of spinneret: dimension 0.08 mm.0.2 mm.

Spinning velocity: -200 m./rnin.

Polymer cone. of spinning solution: 25-35%.

Spinning column length: 5-10 m.

Spinning column temperature: 150-180 C.

Temperature of spinning solution when being discharged from orifice: 70-110 C.

As for the cross linking method of the resulting yarns, there are wet heating method and dry heating method. As a cross linking agent, aldehydes such as formaldehyde acetaldehyde, and dimethylol compounds such as dimethylol urea, dimethylol propylene urea, are used. As a catalyst, an acidic catalyst such as hydrochloric acid, ammonium chloride, magnesium chloride, zinc nitrate, or the like are effectively used. When the wet heating method is used, the cross linking reaction is carried out at a condition of the cross linking agent concentration being 5 to 40 percent (especially preferable when it is more than 10 percent) and the temperature being 50 to 100 C. for 1 to 10 minutes. After this reaction the yarns are washed with Water, followed by drying. When the dry heating method is used, the yarns are immersed in a bath of the above-mentioned cross linking agent for a short time and then they are heated at a temperature of 50 to C. In these cross linking reactions the cross linking between urea linkages is predominant and cross linking between urethane linkages or between urethane linkages and urea linkages hardly occurs. In order that those skilled in the art may more fully understand the nature of this invention and the method of carrying it out, the following examples are given but they are not intended to be unduly limitative of the invention.

The term creep recovery as used in the specification and claims is designated by the following equation:

wherein L represents the initial length of an elastic fi-ber, and AL represents LL and L represents a length of the fiber obtained by loading, to the fiber having the initial length L a weight by which the fiber is drawn up vto length of 3 in a draw rate of 100% per minute, and setting the loading fiber for 30 minutes at the 3 state and thereafter removing the load and allowing to stand the unloaded fiber at the unloading state for 30 minutes, provided these procedures are carried out at 20 C.

The invention is illustrated but not limited by the following examples.

Example 1.-340 g. of polyvalerolactone having an average molecular Weight of 1,700, and whose terminal groups are fixed by propylene oxide; and 100 g. of 4,4- diphenylrnethane diisocyanate are reacted at 95 C. for 120 minutes under a nitrogen atmosphere with stirring. The reaction is completed when the concentration of diisocyanate reaches-1.175 mm./ g. After cooling the reaction mixture to room temperature, 600 g. of purified dimethylformarnide are added thereto, and stirred at a temperature between 28 and 30 C. to produce a homogenous solution.

Then the resulting solution is added to 50 cc. of dimethylformamide solution containing 21.8 g. of ethanolamine with stirring over 10 minutes. The temperature of the solution rises by about C. Then 45.6 g. of diphenylmethane diisocyanate are added thereto in solid form. After stirring at room temperature for 30 minutes, the mixture is kept for 30 hours in a constant temperature room of 28 C. To the solution thus obtained which does not show mobility now, dimethylformamide is further added to give a viscous solution having a polymer concentration of 18 percent. Viscosity of this solution is 38,000 cp. (30 C.). This colorless and transparent spinning solution is extruded through nozzles having 26 holes of 0.1mm. 5 into a coagulation bath (3 percent aqueous solution of sodium carbonate) kept at 60 C. with a.

spinning velocity of 20 m./ min.

Yarn thus obtained is washed with cold water for one hour, and dried at 30 C. for hours- Resulting yarn possesses the following properties.

Tensile strength g./d 0.68 Tensile elongation percent 630 Creep recovery do 95 Subsequently the above-mentioned spun raw yarn is immersed in an aqueous solution of 30 percent Formalin and 0.5 percent ammonium chloride at 90 C. for 2 minutes, washed with water and dried at 50 C. for one hour. Thequality of resulting yarn is further improved and becomes insoluble in dimethylformamide. Properties of yarn are as follows:

Tensile strength g./d 0.75 Tensile elongation percent 640 Creep recovery do 99 Aging effect is found very slight by fadeometer.

Example 2.-36 g. of polybutylene adipate having an 7 average molecular weight of 1800 and 5.20 g. of 2,4- tolylene diisocyanateare introduced into a 300 cc. separable flask equipped with a nitrogen inlet pipe and a stirrer. The mixture is heated at 98 C. for 65 minutes under a nitrogen atmosphere. After cooling the reaction mixture to 30 C., 150 g. of'tfreshly purified dimethylformamide is added thereto and stirred sufficiently to form a homogenous solution. After stirring further for 60 minutes, the resulting solution is added to 50 cc. of dimethylformaldehyde containing 0.61 g. of ethanolamine over 30 minutes with vigorous stirring.

Then 1.25 g. of 4,4'-diphenylmethane diisocyanate are added thereto and after stirring for 45 minutes under a nitrogen atmosphere, the solution is kept for 45 minutes in a constant temperature room of28 C. The spinning solution thus obtained has a viscosity of greater than Tensile strength -g./d 0.65 Tensile elongation percent 680 Creep recovery do 93 When the above-mentioned raw-yarn is subjected to a cross linking treatment as in Example 1, the properties of yarn become as follows:

Tensile strength g./d- 0.72 Tensile elongation percent 670 Creep recovery 'do 99 Insoluble in hot dimethylformami-de.

Decrease of tensile strength is slight by the fadeometer test.

Light fastness is good.

Example 3.--26 g. of valerolactone having an average molecular weight of. 1300 and 10 g. of 4,4'diphenylmethane diisocyanate are introduced into a 300 cc. threeneck flask equipped with a stirrer and a nitrogen inlet pipe, and is heated at a temperature between 98 C. for

minutes in a nitrogen gas stream. After cooling the reaction mixture 90 g. of newly distilled dimethylformamide is added thereto at 40C. and stirred at room temperature further'for 60 minutes. After quantitative analysis for isocyana'te radical precisely, the resultant solution is added to 30 g. of dimethylformamide containing propanolarnine equivalent to the determined value of the isocyanate radical over 15 minutes with vigorousstirring. Then 4,-4-diphenylmethane diisocyanate is added thereto in an amount corresponding to /2 mol of propanolamine added. If. the solution is kept at a temperature of 28 C. for 3 days after suflicient stirring, a viscous solution having viscositygreat-er than 100,000 cp. at 20 C. is obtained. In order to make it readily spinnable, it is diluted with dimethyl formamide until the viscosity becomes 2- 30,000 op. and subjected to spinning as in Example 2. The yarn thus spun is washed with water and subjected to a cross linking treatment as in Example 1 except that Formalin and ammonium chloride in Example 1 are replaced by dimethylol ethylene urea and magnesium chloride respectively. The yarn obtained exhibits the following properties.

Tensile strength g./d 0.78 Tensile elongation percent 670 CI66P recovery do 99.5

Aging by. fadeorneter is slight. Completely insoluble in hot dimethylformamide.

Example 4.46 g. of polytetrahydrofurane having an, average molecular weight of 2300 and 6.7 g. of

1,6-hexamethylene diisocya-nate are made into a pro-- polymer by using the same apparatus and the same method as in Example 2, cooled to 60 C., added to g. of dimethylformamide, and after being stirred for 2 hours at a temperature of 30 C., the remaining isocyanate radical is analysed quantitatively. Then a dimethyl sulfoxide solution of the resulting prepolymer is added to 50 cc. of dimethyl sulfoxide containing 1.22 g. of ethanolamine over 30 minutes with stirring. 1.21 g. of 4,4-di.-

Fastness to light and fastness to solvent are both excellent.

Example 5.38.7 g. of caprolactone-ethylene oxide copolymer having OH number of 107 and containing 20 mole percent of ethylene oxide and 12.90 g. of 4,4- diphenylmethane diisocyanate are added to 150 g. of dehydrated and purified dimethylformamide and stirred at 31 C.- -0.5 C. for 4 hours in a nitrogen atmosphere. Then the resultant solution is added to 47 g. of dimethylformamide containing 1.55 g. of ethanolamine while sufiiciently stirring and after 30 minutes 3.31 g. of 4,4- diphenylmethane diisocayanate are added thereto. The solution thus obtained is stirred at 31 C.i0.5 C. for 4 hours and is left in a constant temperature room of 35 C. for 32 hours and subsequently spun in the same procedure as in Example 2. Yarn dried at 110 C. for one hour exhibits the following properties.

Tensile strength g./d 0.75 Tensile elongation percent 6 90 Creep recovery do 96.5

What We claim is:

1. A polyurethane elastic yarn having a creep recovery above 90% and an intrinsic viscosity between 0.8 and 1.2 'when measured in dimethyl formamide and consisting of a polymer having solely the repeating structural units of the formula o 0 o 0 H H I! II II 10 polymer residue having a molecular weight between 800 and 2500 and a melting point below about 50 C.

3. A method for producing polyurethane elastic yarn, said method comprising reacting a linear bifunctional hydroxyl-terminated polymer having a molecular Weight between 800 and 2500 and a melting point below about 50 C. with an organic diisocyanate, the molar ratio of the isocyanate radical to the hydroxyl radical being 1.02.0: 1.0 to produce an isocyanate-terminated prepolymer, adding at least one organic solvent to said isocyanateterminated prepolymer to prepare a prepolymer solution, reacting the prepolymer in solution with an aminoalcohol in a molar amount equivalent to the isocyanate radical of said prepolymer to produce a low molecular 15' weight hydroxyl-terminated polymer, reacting said low molecular weight hydroxyl-terminated polymer with an organic diisocyanate, the molar ratio of the isocyanate radical to the hydroxyl radical in said low molecular weight hydroxyl-terminated polymer being 1.001.04: 1.00

to produce a polyurethane polymer and extruding the polyurethane polymer through an orifice to produce a polyurethane elastic yarn.

4. A method for producing polyurethane elastic yarn having a creep recovery above 90% and a cross linked structure said method comprising reacting a linear bifunct-ional hydroxyl-terminated polymer having a molecular Weight between 800 and 2500 and a melting point below about 50 C. with an organic diisocyanate, the molar ratio of the isocyanate radical to the hydroxyl radical being 1.02.0:1 to produce an isocyanate-termiwherein R is a bivalent organic radical selected from the group consisting of 1,3-phenylene, 1,4-phenylene, 2,4- tolylene, 2,6-tolylene, 4,4'-biphenylene, 2,2-dimethyl-4,4'- biphenylene, 3,3 dimethyl 4,4 biphenylene, 4,4'-diphenylmethane, 3,3'-dimethyl-4,4-diphenylmethane, 1,5- naphthylene, 1,8-naphthylene, trimethylene, tetramethylene, pentamethylene and hexamethylene radicals; R is a bivalent organic radical selected from the group consisting of ethylene, propylene, iso-propylene and n-butylene radicals; A is a bivalent polymer residue selected from the group consisting of polyester residue, polyether residue and poly (oxyalkylenecarboxyalkylene) residue having a molecular weight between 800 and 2500' and a melting point below about 50 C.

2. A polyurethane elastic yarn of a cross-linked struc ture having at least partly intermolecular cross-linkages formed by connecting mainly a urea linkage with another urea linkage by condensing said urea linkages with one member selected from the group consisting of formaldehyde, acetaldehyde, dimethylol urea and dimethylol propylene urea in the polymer consisting of a polymer having solely the repeating structural units of the formula:

0 O O O 0 II II II II nated prepolymer, adding at least one organic solvent to said isocyanate-terminated prepolymer to prepare a prepolymer solution, reacting the prepolymer in solution 40 with an aminoalcohol, the molar ratio of the isocyanate radical of the prepolymer to said aminoalcohol being 1:1 to produce a low molecular Weight hydroxyl-terminated polymer, reacting said low molecular Weight hydroxyltermina-ted polymer with an organic diisocyanate, the

molar ratio of the isocyanate radical to said hydroxyl- C. and 120 C. in the presence of a cross linking agent selected from the group consisting of formaldehyde, acetaldehyde, and dimethylol ureas and an acidic catalyst.

5. A method according to claim 3 wherein the linear bifunctional hydroxyl-terminated polymer is selected from the group consisting of polyester glycol, polyether glycol and poly(oxyalkylene-carboxalkylene) glycol.

6. A method according to claim 3 wherein the organic diisocyana-te is selected from the group consisting of 1,3-

wherein R is a bivalent organic radical selected from the group consisting of 1,3-phenylene, 1,4-phenylene, 2,4- tolylene, 2,6-tolylene, 4,4'-biphenylene, 2,2'-dimethyl- 4,4'-biphenylene, 3,3'-dimethyl-4,4'-biphenylene, 4,4'-diphenylmethane, 3,3-dimethyl-4,4'-diphenylmethane, 1,5- naphthylene, 1,8-naphthylene, trimethylene, tetramethylene, pentamethylene and hexamethylene radicals; R is a bivalent organic radical selected from the group consisting of ethylene, propylene, iso-propylene and n-butylene radicals; A is a bivalent polymer residue selected from the group consisting of polyester, polyether and poly (oxyalkylene-carboxyalkylene) residues, said bivalent 75 phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-

tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4bi-

isocyanate, pentamethylene diisocyanate and hexamethylene diisocyanate.

7. A method according to claim 3 wherein the aminoalcohol is selected from the group consisting of ethanolamine, propanolamine, iso-propanolamine, and n-butanolamine.

8. A method according to claim 3 wherein the organic solvent is selected from the group consisting of dioxane, acetone, methylethyl ketone, benzene, toluene, dirnethyl torma-mide, diethyl acetamide and dimethyl sulfoxide.

9. A method according to claim 4 wherein the linear b'itunctional hydroXyl-terminated polymer is selected from the group consisting of polyester glycol, polyether glycol and poly(oxyalkylene-carboxyalkylene) glycol.

10. A method according to claim 4 wherein the organic diisocyanate is selected from the group consisting of 1,3- phenylene diisocyan-ate, 1,4-phenylene diisocyanate, 2,4- tolylene diisocyanate, 2,6-tolylene di-isocyanate, 4,4-biphenylene diisocyanate, 2,2'-dirnethyl-4,4-biphenylene d iisocyanate, 3,3-dimethyl-4,4-diphenylmethane diisocyan ate, 1,5-naphthylene diisocyan-ate, 1,8-naphthylene di-' isocyanarte, trimethylene diisocyan-ate, tetramethylene diisocyanate,pentarnethylene diisocyanate and hexamethylene diisocyanate.

11. A method according to claim 4 wherein the aminoalcohol is selected from the group consisting of ethanolarnine, propanolamine, iso-propanol'amine and n-butanolamine.

12. A method according to claim 4 wherein the organic solvent is selected from the group consisting of dioxane, acetone, methylethyl ketone, benzene, toluene, dimethyl formamide, ,diethyl a-cetamide and dimethyl sulfoxide.

References Cited UNITED STATES PATENTS 3,087,912 4/1963 Wagner et al. 260-75 3,148,173 9/1964 Axelrood 260-4550 3,149,998 9/1964- Thurmaier 260-775 3,184,426 5/1965 Thomas et al. 26077.5

MURRAY TILLMAN, Primary Examiner.

J. C. BLEUTGE, Assistant Examiner. 

1. A POLYURETHANE ELASTIC YARN HAVING A CREEP RECOVERY ABOVE 90% AND AN INTRINSIC VISCOSITY BETWEEN 0.8 AND 1.2 WHEN MEASURE IN DIMETHYL FORMAMIDE AND CONSISTING OF A POLYMER HAVING SOLELY THE REPEATING STRUCTURAL UNITS OF THE FORMULA -A-OOC-NH-R-NH-CO-NH-R''-OOC-NH-R-NH-COO-R''-NH-CO-NHR-NH-COOWHEREIN R IS A BIVALENT ORGANIC RADICAL SELECTED FROM THE GROUP CONSISTING OF 1,3-PHENYLENE, 1,4-PHENYLENE, 2,4TOLYLENE, 2,6-TOLYLENE, 4,4''-BIPHENYLENE, 2,2''-DIMETHYL-4,4''BIPHENYLENE, 3,3''-DIMETHYL-4,4-BIPHENYLENE, 4,4''-DIPHENYLMETHANE, 3,3''-DIMETHYL-4,4''-DIPHENYLMETHANE, 1,5NAPHTHYLENE, 1,8-NAPHTHYLENE, TRIMETHYLENE, TETRAMETHYLENE, PENTAMETHYLENE AND HEXAMETHYLENE RADICALS; R'' IS A BIVALENT ORGANIC RADICAL SELECTED FROM THE GROUP CONSISTING OF ETHYLENE, PROPYLENE, ISO-PROPYLENE AND N-BUTYLENE RADICALS; A IS A BIVALENT POLYMER RESIDUE SELECTED FROM THE GROUP CONSISTING OF POLYESTER RESIDUE, POLYETHER RESIDUE AND POLY (OXYALKYLENECARBOXYALKYLENE) RESIDUE HAVING A MOLECULAR WEIGHT BETWEEN 800 AND 2500 AND A MELTING POINT BELOW ABOUT 50*C. 